1. Field of the Invention
The present invention relates to an etching apparatus, and more particularly, to an apparatus for etching a substrate uniformly by using ultrasonic oscillation.
2. Description of the Related Art
As a display device for a television and a personal computer, a large sized cathode ray tube (CRT) display device is commonly used. However, since the screen must be separated from the electron gun by more than a predetermined distance for a large size screen CRT, the volume of the device is increased. Thus, such a CRT cannot be applied to a low weight, small size, and a low power consumption electronic device, such as a wall-mountable television, a portable television, and a notebook computer.
For a small and light display device, flat panel devices such as a liquid crystal display device (LCD), plasma display panel (PDP), electroluminescent display (ELD) and vacuum fluorescent display (VFD) have been introduced recently. Among the above flat panel display devices, the LCD has been researched extensively for good picture quality and low power consumption. The LCD-applied portable television and notebook computer have been introduced in the market, but there are problems to be solved in such LCD-applied devices. In particular, size and weight are important factors to be considered for the LCD.
For a small size and light LCD, there are several available methods for reducing the size and weight of the LCD element. However, the driving circuit and the thin film transistor, which are necessary elements of the LCD, are so thin that reducing these elements will not affect the weight in any significant manner. On the other hand, it is possible to reduce the weight of the LCD element by reducing the weight of the glass substrate that is a basic element of the LCD. Specifically, since the glass substrate is a heavy element of the LCD, methods of reducing the weight of the glass substrate have been continuously researched.
For a glass substrate of a given surface area, a light glass substrate requires a thin glass substrate. However, known methods of thinning the glass substrate cause damage including internal imperfections and surface roughness. Thus, the mechanical strength of the glass substrate is weakened, and the image quality of the LCD is accordingly deteriorated.
Conventionally, the most common method of reducing the weight of the glass substrate is to etch the surface of the glass substrate by soaking the substrate in a container having an etchant. In this method, however, the substrate is often not etched uniformly because of the non-uniform surface of the substrate. Further, the impurities generated during the etching process often attach to the surface of the substrate so that the resulting surface becomes even rougher.
To solve the aforementioned problems, the substrate is placed in a container having an etchant and then bubbles are generated and directed through a porous plate to the surface of the substrate in order to remove the impurities attached to the surface of the substrate, and a fresh etchant is applied to the surface of the substrate.
FIG. 1 is a sectional view showing a related art apparatus for etching a glass substrate that is etched in a method employing nitrogen bubbles.
For reference, the related art was filed by the Applicant of the present invention as U.S. patent application Ser. No. 09/389,959. Therefore, the present invention is an improvement of the related art.
As shown in FIG. 1, a teflon cassette 117 maintaining fixed spaces is formed in the interior of etching bath 111 filled with etchant 121. The height of the etchant 121 is lower than that of the etching bath 111 so that the etchant cannot flow out to the outside. In the teflon cassette 117, a substrate 119 including a color filter substrate and a thin film transistor (TFL) substrate is supported by a support means (not shown in the figures). A nitrogen bubble generation pipe 113 is formed on the lower portion of the teflon cassette 117 so that nitrogen bubbles 123 are supplied through a plurality of the nitrogen bubble generation tubes 115. The supplied nitrogen bubbles 123 rise along the surface of the substrate 119 so that the impurities generated during the photolithography process and adhering to the substrate surface are removed. In this type of etching process, the extent of etching of the substrate 119 depends on, and therefore can be determined by, the temperature obtained from an exothermic reaction that is generated between the etchant 121 and the substrate 119.
In this related art method, however, since the bubbles, necessarily having different sizes, are applied on the upper portion and lower portion of the substrate, there is a resultant thickness difference between the upper portion and lower portion. As a result, the substrate is still easily damaged even by light force during the LCD process because of the non-uniformity of the thickness of the substrate. Further, the substrate must be soaked for a long period, for example, scores of minutes, to etch the substrate sufficiently. Thus, the processing cost is increased in this method.